Tough soluble aromatic thermoplastic copolyimides

ABSTRACT

Tough, soluble, aromatic, thermoplastic copolyimides were prepared by reacting 4,4&#39;-oxydiphthalic anhydride, 3,4,3&#39;,4&#39;-biphenyltetracarboxylic dianhydride and 3,4&#39;-oxydianiline. Alternatively, these copolyimides may be prepared by reacting 4,4&#39;-oxydiphthalic anhydride with 3,4,3&#39;,4&#39;-biphenyltetracarboxylic dianhydride and 3,4&#39;-oxydiisocyanate. Also, the copolyimide may be prepared by reacting the corresponding tetra acid and ester precursors of 4,4&#39;-oxydiphthalic anhydride and 3,4,3&#39;,4&#39;-biphenyltetracarboxylic dianhydride with 3,4&#39;-oxydianiline. These copolyimides were found to be soluble in common amide solvents such as N,N&#39;-dimethyl acetamide, N-methylpyrrolidinone, and dimethylformamide allowing them to be applied as the fully imidized copolymer and to be used to prepare a wide range of articles.

ORIGIN OF THE INVENTION

The invention described herein was made by an employee of the UnitedStates Government, and may be manufactured and used by or for theGovernment without payment of any royalties thereon or therefor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application from commonlyowned patent application Ser. No. 09/062,082, filed Apr. 17, 1998, nowabandoned which is a continuation patent application of Ser. No.08/359,752, filed Dec. 16, 1994, now U.S. Pat. No. 5,741,883.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to copolyimides. In particular, it relatesto soluble copolyimides prepared from 4,4'-oxydiphthalic anhydride,3,4,3',4'-biphenyltetracarboxylic dianhydride and 3,4'-oxydianiline. Itrelates also to these same soluble copolyimides prepared from4,4'-oxydiphthalic anhydride, 3,4,3',4'-biphenyltetracarboxylicdianhydride and 3,4'-oxydiisocyanate. It furthermore relates to thesecopolyimides prepared from reacting the corresponding tetra acid andester precursors to 4,4'-oxydiphthalic anhydride and3,4,3',4'-biphenyltetracarboxylic dianhydride with 3,4'-oxydianiline.

2. Description of the Related Art

Aromatic, thermoplastic polyimides are a class of polymers used in avariety of high performance/high temperature applications. Suchapplications include adhesives, matrix resins for composites, and highstrength films and coatings. These thermoplastic polyimides are usuallysoluble in either high boiling polar protic phenolic solvents, such asm-cresol and chlorophenol or halogenated solvents such astetrachloroethylene and multihalogenated aromatics, many of which arehighly toxic and are not used in large scale industrial processeswithout solvent recovery systems. Thus, the majority of polyimidethermoplastics are solution processed in the polyamic acid state usingmilder solvents and subsequently cyclodehydrated to form the finalpolyimide article. However, there is a disadvantage to using thepolyamic acid intermediates in that they are unstable, susceptible tohydrolysis, and generate water during imidization.

Attempts to increase the solubility of polyimides generally involve themodification of the polymer backbone through monomer selection. Thesemodifications include the incorporation of flexible aliphatic units,polar and nonpolar pendent substituents, heteroatoms or groups, andpolyimide copolymers which contain either mixtures of the above monomerswith common aromatic diamines and dianhydrides, or block segments ofsoluble oligomers. Although most of these polyimides meet and evenexceed some of the criteria required to find wide spread use as highperformance materials, cost limits their acceptance.

By the present invention, wholly aromatic, thermoplastic polyimidecopolymers were prepared based on 4,4'-oxydiphthalic anhydride,3,4,3',4'-biphenyltetracarboxylic dianhydride and 3,4'-oxydianiline.These copolyimides were found to be tough thermoplastics which aresoluble in common amide solvents such as N,N'-dimethyl acetamide (DMAc),N-methylpyrrolidinone (NMP), and dimethyl formamide (DMF) and thus canbe applied as the fully imidized copolymer in addition to the amic acidsolution.

Meterko et al. (U.S. Pat. No. 5,171,828) had prepared copolyimides from4,4'-oxydiphthalic anhydride, 3,4,3',4'-biphenyltetracarboxylicdianhydride and 4,4'-oxydianiline or para-phenylenediamine. Thedifference between the present invention and that of Meterko et al. liesin the use of 3,4'-oxydianiline as compared to 4,4'-oxydianiline.Meterko et al. prepared polyimide films by pouring the polyamic acidinto the desired form. The polyamic acid was then cured either byheating or through chemical imidization. Meterko et al. found that theircopolyimides had unexpectedly high comparative tracking indexes whichmade the copolyimides useful as insulators for various electronicapplications. It is important to note that Meterko et al. applied theircopolyimide as a polyamic acid prior to imidizing and not as an imidizedsolution.

St. Clair et al. (U.S. Pat. No. 5,147,966) prepared polyimide moldingpowders, coatings, adhesives and matrix resins from 3,4'-oxydianilineand 4,4'-oxydiphthalic anhydride. They found that by preparingpolyimides and polyamic acids from these monomers, along with suitableendcaps, adhesives, composite matrix resins, neat resin moldings, andfilms or coatings had identical or superior properties to commerciallyavailable polyimides. Unfortunately, as with Meterko et al., thesepolyimide homopolymers were applied as the amic acid solution.

Tamai et al. (U.S. Pat. No. 5,268,446) prepared readily melt-processablepolyimides by reacting 3,3',4,4'-biphenyltetracarboxylic dianhydridewith 3,4'-oxydianiline. They found that these polyimides had excellentprocessability and chemical resistance in addition to essential heatresistance. These polymers may be used in various fields such aselectric and electronic appliances, space and aeronautical equipment andtransportation machinery. They note in example 1 that the polyimide wasinsoluble in halogenated hydrocarbon solvents such as methylene chlorideand chloroform. In addition, they prepared films from the amic acidsolution instead of from the imide powder.

An object of the present invention is to prepare a tough, soluble,aromatic, thermoplastic copolyimide.

Another object of the invention is to prepare a diverse group ofarticles from the copolyimide.

SUMMARY OF THE INVENTION

The foregoing and additional objects of the invention were achieved bypreparing a tough, soluble, aromatic, thermoplastic copolyimide byreacting 4,4'-oxydiphthalic anhydride with3,4,3',4'-biphenyltetracarboxylic dianhydride and 3,4'-oxydianiline.Alternatively, the tough, soluble aromatic thermoplastic copolyimide maybe prepared by reacting 4,4'-oxydiphthalic anhydride with3,4,3',4'-biphenyltetracarboxylic dianhydride and 3,4'-oxydiisocyanate.Also, the copolyimide may be prepared by reacting the correspondingtetra acid and ester precursors of 4,4'-oxydiphthalic anhydride and3,4,3',4'-biphenyltetracarboxylic dianhydride with 3,4'-oxydianiline.

The tough, soluble, aromatic, thermoplastic copolyimide may be used toprepare the following articles: a solvent cast film, an extrudableobject, a fiber-reinforced composite, a neat resin molding, a coating, ahot-melt adhesive film, a hot-melt adhesive cloth, a hot-melt adhesivetape, a fiber, a filled resin molding and a matrix composite. The matrixcomposite further comprises a powder. As a preferred embodiment, thispowder is selected from the group consisting of: plastic, metal,graphite and ceramic. The tough, soluble, aromatic thermoplasticcopolyimide may furthermore be used as a foam, a tack-free recastablefilm, and a praticle filled thin film and coating. As a preferredembodiment, this particle is selected from the group consisting of:metals, plastics, ceramics and non-metallics such as carbon and boronand any combination thereof.

The copolyimide of the present invention may be terminated with either amonofunctional anhydride or a monofunctional amine endcapper. Theendcapper is added to the copolyimide at an amount ranging from about 2mole percent to about 10 mole percent. An example of this endcapper isphthalic anhydride. Other endcappers include: maleic anhydride,phenylethynyl anhydride, ethynyl anhydride, nadic anhydride, vinylicanhydride, allylic anhydride, benzocyclobutane anhydride, phenylethynylamine, ethynylaniline, vinylaniline and allylaniline. These endcappedcopolyimides may be used to prepare the articles listed above.

The 4,4'-oxydiphthalic anhydride and the3,4,3',4'-biphenyltetracarboxylic dianhydride are added to the3,4'-oxydianiline at a ratio of 4,4'-oxydiphthalic anhydride to3,4,3',4'-biphenyltetracarboxylic dianhydride ranging from about 25 molepercent to about 75 mole percent (25:75) to about 75 mole percent toabout 25 mole percent (75:25). These copolyimides may be endcapped witheither a monofunctional anhydride or a monofunctional amine at an amountranging from about 2 mole percent to about 10 mole percent. Thepreferred endcapper is phthalic anhydride. The articles prepared fromthese copolyimides are the same as those listed above.

In particular, the 4,4'-oxydiphthalic anhydride and the3,4,3',4'-biphenyltetracarboxylic dianhydride are added to the3,4'-oxydianiline at a ratio of 50 mole percent 4,4'-oxydiphthalicanhydride to 50 mole percent 3,4,3',4'-biphenyltetracarboxylicdianhydride. An endcapper such as a monofunctional anhydride or amonofunctional amine may also be added to the copolyimide at an amountranging from about 2 mole percent to about 10 mole percent. Preferably,the endcapper is phthalic anhydride. These copolyimides may be used toprepare the articles which are listed above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

By the present invention, a copolyimide was prepared by reacting4,4'-oxydiphthalic anhydride (ODPA) with3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA) and3,4'-oxydianiline (3,4'-ODA). Alternatively, the tough, soluble aromaticthermoplastic copolyimide may be prepared by reacting 4,4'-oxydiphthalicanhydride with 3,4,3',4'-biphenyltetracarboxylic dianhydride and3,4'-oxydiisocyanate. Also, the copolyimide may be prepared by reactingthe corresponding tetra acid and ester precursors of 4,4'-oxydiphthalicanhydride and 3,4,3',4'-biphenyltetracarboxylic dianhydride with3,4'-oxydianiline. This copolyimide has the following repeat unit:##STR1## when ODPA and BPDA are used in equal proportion. It has beenfound to be a tough thermoplastic material. In addition, the copolyimidemay be redissolved in common amide solvents such as DMAc, NMP and DMFafter the imide powder has been formed, provided that the polyimide isnot exposed to temperatures above its glass transition temperature (Tg).(Typically, once a polyamic acid has been converted to the imide, itcannot be redissolved in common amide solvents.) This unique property,allows these copolyimides to be used for a large number of applications.For example films, which were cast from the copolyimide after it hadbeen dissolved in solvent and dried above the Tg were found to exhibithigh modulus, good chemical resistance and be self bonding. The selfbonding property and insolubility above the Tg allows layered films andcoatings to be prepared. These copolyimides can also be extruded whichprovides them with the capability to form a wide range of objects.Because of their unique combination of properties, fiber-reinforcedcomposites can also be prepared from these copolyimides. Coatingsprepared from these copolyimides were successfully used to coat Kapton®,glass, aluminum, copper, ceramic and titanium substrates. It was foundthat these copolyimides are capable of bonding to themselves as well asmany other materials and thus, they are useful as hot-melt adhesivefilms, hot-melt adhesive cloths and hot-melt adhesive tapes. As yetanother application, these copolyimides find utility as neat resinmoldings and filled resin moldings, and can be processed at temperaturesslightly below the Tg of the copolyimide which can be readily machinedand polished. Matrix composites, which can also be processed attemperatures slightly below the Tg of the copolyimide, have beensuccessfully prepared from these copolyimides. These composites wereprepared by combining the copolyimide with whiskers and/or a powder. Anypowder known to those skilled in the art may be used. Examples of thesepowders include but are not limited to: graphite, ceramic, metal,plastic, copper, iron, diamond dust, polyimide powder, boron, aluminum,and chopped carbon fibers. More specifically, ceramic powders such assilicon nitride, quartz, zirconia, mixed oxides and aluminum oxide maybe used. Plastic powders which may be used include any powder which maywithstand the high processing temperature. As a preferred embodiment,the powder may be a plastic, metal, graphite or ceramic powder.Furthermore, these copolyimides find utility as a foam, created fromvolatile evolution at elevated temperatures. Also, these copolyimidesmay be used for a tack-free recastable film, created from solventcontaining tack-free flexible film. Finally, these copolyimides may findutility as a praticle filled thin film and coating, where the particlescan be selected from the group consisting of: metals, plastics, ceramicsand non-metallics such as carbon and boron and any combination thereof.

The degree of solubility of these copolyimides can be controlled by theprocessing conditions used to prepare the copolyimide. Several factorswere found to affect the solubility of the copolyimide. One of thesefactors was the mole ratio of ODPA to BPDA. In addition, the percentageof solids and the solvent used to synthesize the copolyimide was alsofound to have an effect on the solubility. For example, it was observedthat when the ratio of ODPA to BPDA was 75 mole percent to 25 molepercent (75/25), and the copolyimide was prepared at 30% solids in NMP,a turbid gel formed when the solution was cooled to room temperature.However, for the same mole ratio, when a 15% solids solution wasprepared, the copolyimide remained soluble in NMP when the solution wascooled to room temperature. For a 50/50 mole ratio of ODPA to BPDAcopolyimide prepared in NMP, it was found that the copolyimide remainedsoluble and if allowed to remain undisturbed for 6 to 48 hours(depending on the percent solids) formed a thermally and mechanicallyreversible gel when the copolyimide was prepared using up to 60% solids.When DMAc was substituted as the solvent, the copolyimide was soluble at15% solids but precipitated out at 30% solids. As with the 75/25ODPA/BPDA ratio, copolyimides synthesized at a molar ratio of 25/75ODPA/BPDA were found to remain soluble in NMP at 30% solids duringimidization but when cooled to room temperature formed either a turbidgel or an elastomeric homogeneous gel. At 15% solids in NMP, thecopolyimides remained soluble. It was also observed that all of thecopolyimides remained soluble in m-cresol. In addition to controllingthe mole ratio and percent solids, it was found that controlling themolecular weight of the copolyimide affected the sol-gel behavior.

In order to control the molecular weight of these copolyimides, thestoichiometry may be offset and the copolyimide may be terminated withan endcapper such as a monofunctional anhydride or a monofunctionalamine. A preferred endcapper is phthalic anhydride. Other endcappersinclude: maleic anhydride, phenylethynyl anhydride, ethynyl anhydride,nadic anhydride, vinylic anhydride, allylic anhydride, benzocyclobutaneanhydride, phenylethynyl amine, ethynylaniline, vinylaniline andallylaniline. The endcapper may be added to the copolyimide at an amountranging from about 2 mole percent to about 10 mole percent depending onthe desired properties of the copolyimide. The addition of the endcappermay allow for better processing in some instances.

As a preferred embodiment of the invention, it was found that goodresults were obtained when the ODPA and the BPDA were added to the3,4'-ODA at a ratio of ODPA to BPDA ranging from about 25 mole percentto about 75 mole percent (25:75) to about 75 mole percent to about 25mole percent (75:25). More preferably, the best results were obtainedwhen the ratio of ODPA to BPDA was 50 mole percent to 50 mole percent(50:50). The addition of an endcapper such as a monofunctional amine ora monofunctional anhydride allowed for molecular weight control whichprovides versatility in the final end-use of the copolyimides.

An alternative method for making the copolyimide allows for thereplacement of the diamine with a diisocyanate. In the instant case,3,4'-oxydiisocyanate is used in place of 3,4'-oxydianiline. Thus, thetough, soluble aromatic thermoplastic copolyimide may be prepared byreacting 4,4'-oxydiphthalic anhydride with3,4,3',4'-biphenyltetracarboxylic dianhydride and 3,4'-oxydiisocyanate.

Yet another method for making the copolyimide requires the replacementof the dianhydrides with their correpsonding tetra acid or esterprecursors. This procedure affords an intermediate organic salt which isimidized in the melt or in solution through the application of heat. Theadvantage is that these acids and esters are the starting materials toafford the corresponding dianhydrides. Hence, the additional chemicalreactions and purification procedures required to generate thedianhydrides from the tetra-acids can be avoided. In a similar manner,the conversion to the tetra-esters by treating the tetra acids with therequired alcohol affords a viscous monomer system, which can beconverted, to the polyimide through the application of heat. Thus, thetough, soluble aromatic thermoplastic copolyimide may be prepared byreacting the corresponding tetra acid or ester precursors of4,4'-oxydiphthalic anhydride and 3,4,3',4'-biphenyltetracarboxylicdianhydride with 3,4'-oxydianiline.

The following examples illustrate the preparation and use of thecopolyimides. These examples are merely illustrative and intended toenable those skilled in the art to practice the invention in all of theembodiments flowing therefrom, and do not in any way limit the scope ofthe invention as defined by the claims.

EXAMPLES Example 1

In a 500 mL resin kettle equipped with a nitrogen inlet, overheadstirring assembly, Dean-Stark trap, and condenser were placed ODPA(commercially available from Imitec, Inc.) (17.0257 g, 0.0549 mol), BPDA(commercially available from Ube Industries, Inc.) (5.4137 g, 0.0184mol), 3,4'-ODA (commercially available from Mitsui Toatsu Chemical Co.)(15.0231 g, 0.07502 mol), phthalic anhydride (0.4533 g, 0.00306 mol) andNMP (216 g). The solution was stirred overnight at room temperature.Toluene (50 g) was added to the solution and the mixture was heated to165° C. for 7 hours during which time water was removed by azeotropicdistillation. The reaction was cooled to room temperature. The solutionwas forced through a 5 μm filter. The copolyimide was precipitated usingwater and chopped in a blender. The resulting polymer powder (brightyellow in color) was collected by filtration, extracted with methanolfor 48 hours and dried in vacuo at 200° C. for 9 hours.

Example 2

In a 100 mL resin kettle equipped with a nitrogen inlet, overheadstirring assembly, Dean-Stark trap, and condenser were placed ODPA(15.9407 g, 0.0514 mol), BPDA (5.0395 g, 0.0171 mol), 3,4'-ODA (14.1435g, 0.0706 mol), phthalic anhydride (0.6277 g, 0.0042 mol) and NMP (81.5g). The solution was stirred overnight at room temperature. Toluene (20g) was added to the solution and the mixture was heated to 165° C. for 7hours during which time water was removed by azeotropic distillation.The reaction was cooled to room temperature forming a turbid gel. Thecopolyimide was precipitated in water and chopped with a blender. Theresulting polymer powder (bright yellow in color) was collected byfiltration, extracted with methanol for 48 hours and dried in vacuo at200° C. for 9 hours.

Example 3

In a 500 mL resin kettle equipped with a nitrogen inlet, overheadstirring assembly, Dean-Stark trap, and condenser were placed ODPA(16.0239 g, 0.05165 mol), BPDA (15.1975 g, 0.05165 mol), 3,4'-ODA(20.6862 g, 0.1033 mol) and NMP (120 g). The solution was stirredovernight at room temperature forming a heavy gel. Toluene (25 g) wasadded to the solution and the mixture was heated to 165° C. for 7 hours,during which time water was removed by azeotropic distillation. Thereaction was cooled to room temperature. The solution was forced througha 5 μm filter. The remaining copolyimide powder was precipitated usingwater and chopped in a blender. The resulting polymer powder (brightyellow in color) was collected by filtration, extracted with methanolfor 48 hours and dried in vacuo at 200° C for 12 hours.

Example 4

In a 1 L resin kettle equipped with a nitrogen inlet, overhead stirringassembly, Dean-Stark trap and condenser were placed ODPA (35.8835 g,0.1156 mol), BPDA (34.0329 g, 0.1156 mol), 3,4'-ODA (46.7922 g, 0.2367mol), phthalic anhydride (0.6922 g, 0.00467 mol) and NMP (274 g). Thesolution was stirred overnight at room temperature. Toluene (50 g) wasadded to the solution and the mixture was heated to 165° C. for 7 hours,during which time water was removed by azeotropic distillation. Thereaction was cooled to room temperature. The solution was forced througha 5 μm filter. The copolyimide was precipitated using water and choppedin a blender. The resulting polymer powder (bright yellow in color) wascollected by filtration, extracted with methanol for 48 hours and driedin vacuo at 180° C for 9 hours.

Example 5

In a 1 L resin kettle equipped with a nitrogen inlet, overhead stirringassembly, Dean-Stark trap and condenser were placed ODPA (213.13 g,0.6870 mol), BPDA (202.14 g, 0.6870 mol), 3,4'-ODA (280.76 g, 1.4020mol), phthalic anhydride (8.3072 g, 0.0561 mol) and NMP (1640 g). Thesolution was stirred overnight at room temperature. Toluene (300 g) wasadded to the solution and the mixture was heated to 165° C. for 7 hours,during which time water was removed by azeotropic distillation. Thereaction was cooled to room temperature. The solution was forced througha 5 μm filter. The copolyimide was precipitated using water and choppedin a blender. The resulting copolyimide powder (bright yellow in color)was collected by filtration, extracted with methanol for 48 hours anddried in vacuo at 180° C. for 9 hours.

Example 6

In a 1 L resin kettle equipped with a nitrogen inlet, overhead stirringassembly, Dean-Stark trap, and condenser were placed ODPA (39.2347 g,0.1265 mol), BPDA (37.2112 g, 0.1265 mol), 3,4'-ODA (51.6841 g, 0.2581mol), phthalic anhydride (1.5292 g, 0.0132 mol) and DMAc (740 g). Thesolution was stirred overnight at room temperature. Toluene (100 g) wasadded to the solution and the mixture was heated to 165° C. for 7 hoursduring which time water was removed by azeotropic distillation. Thereaction was cooled to room temperature. The solution was forced througha 5 μm filter. The copolyimide was precipitated using water and choppedin a blender. The resulting polymer powder (bright yellow in color) wascollected by filtration, extracted with methanol for 48 hours and driedin vacuo at 200° C. for 12 hours.

Example 7

In a 1 L resin kettle equipped with a nitrogen inlet, overhead stirringassembly, Dean-Stark trap, and condenser were placed ODPA (3.6850 g,0.01246 mol), BPDA (3.6656 g, 0.01246 mol), 3,4'-ODA (5.0922 g, 0.02543mol), phthalic anhydride (0.1506 g, 0.00102 mol) and m-cresol (38 g).The solution was stirred overnight at room temperature forming a slurry.The mixture was heated to 195° C. for 6 hours. The reaction was cooledto room temperature. The solution was forced through a 5 μm filter. Thecopolyimide was precipitated using methanol and chopped in a blender.The resulting copolyimide powder (bright yellow in color) was collectedby filtration, extracted with methanol for 48 hours and dried in vacuoat 180° C. for 9 hours.

Example 8

In a 1 L resin kettle equipped with a nitrogen inlet, overhead stirringassembly, Dean-Stark trap, and condenser were placed ODPA (38.8358 g,0.1251 mol), BPDA (36.8329 g, 0.1251 mol), 3,4'-ODA (15.6861 g, 0.2581mol), phthalic anhydride (2.2939 g, 0.0155 mol) and NMP (303 g). Thesolution was stirred overnight at room temperature. Toluene (23 g) wasadded to the solution and the mixture was heated to 165° C. for 7 hoursduring which time water was removed by azeotropic distillation. Thereaction was cooled to room temperature. The solution was forced througha 5 μm filter. The copolyimide was precipitated using water and choppedin a blender. The resulting polymer powder (bright yellow in color) wascollected by filtration, extracted with methanol for 48 hours and driedin vacuo at 200° C. for 9 hours.

Example 9

In a 1 L resin kettle equipped with a nitrogen inlet, overhead stirringassembly, Dean-Stark trap, and condenser were placed ODPA (40.3856 g,0.1301 mol), BPDA (38.3028 g, 0.1301 mol), 3,4'-ODA (55.4641 g, 0.2769mol), phthalic anhydride (4.9232 g, 0.03324 mol) and NMP (325 g). Thesolution was stirred overnight at room temperature. Toluene (35 g) wasadded to the solution and the mixture was heated to 165° C. for 7 hoursduring which time water was removed by azeotropic distillation. Thereaction was cooled to room temperature. The solution was forced througha 5 μm filter. The copolyimide was precipitated using water and choppedin a blender. The resulting polymer powder (bright yellow in color) wascollected by filtration, extracted with methanol for 48 hours and driedin vacuo at 180° C. for 9 hours.

Example 10

In a 1 L resin kettle equipped with a nitrogen inlet, overhead stirringassembly, Dean-Stark trap, and condenser were placed ODPA (41.1663 g,0.1327 mol), BPDA (39.0432 g, 0.1327 mol), 3,4'-ODA (55.9411 g, 0.2793mol), phthalic anhydride (4.1379 g, 0.02794 mol) and NMP (327 g). Thesolution was stirred overnight at room temperature. Toluene (30 g) wasadded to the solution and the mixture was heated to 165° C. for 7 hours,during which time water was removed by azeotropic distillation. Thereaction was cooled to room temperature. The solution was forced througha 5 μm filter. The copolyimide was precipitated using water and choppedin a blender. The resulting polymer powder (bright yellow in color) wascollected by filtration, extracted with methanol for 48 hours and driedin vacuo at 180° C for 9 hours.

Example 11

In a 500 mL resin kettle equipped with a nitrogen inlet, overheadstirring assembly, Dean-Stark trap, and condenser were placed ODPA(5.9869 g, 0.0193 mol), BPDA (17.0345 g, 0.0579 mol), 3,4'-ODA (15.7326g, 0.07877 mol), phthalic anhydride (0.4667 g, 0.00315 mol) and NMP (225g). The solution was stirred overnight at room temperature. Toluene (50g) was added to the solution and the mixture was heated to 165° C. for 7hours, during which time water was removed by azeotropic distillation.The reaction was cooled to room temperature. The solution was forcedthrough a 5 μm filter. The copolyimide was precipitated using water andchopped in a blender. The resulting polymer powder (bright yellow incolor) was collected by filtration, extracted with methanol for 48 hoursand dried in vacuo at 200° C for 9 hours.

Example 12

In a 100 mL resin kettle equipped with a nitrogen inlet, overheadstirring assembly, Dean-Stark trap, and condenser were placed ODPA(5.5076 g, 0.01775 mol), BPDA (15.6707 g, 0.05326 mol), 3,4'-ODA(14.5104 g, 0.07246 mol), phthalic anhydride (0.4293 g, 0.0029 mol) andNMP (84 g). The solution was stirred overnight at room temperature.Toluene (15 g) was added to the solution and the mixture was heated to165° C. for 7 hours during which time water was removed by azeotropicdistillation. The reaction was cooled to room temperature forming asolid gel. The gel was placed in water and chopped with a blender. Theresulting polymer powder (bright yellow in color) was collected byfiltration, extracted with methanol for 48 hours and dried in vacuo at200° C. for 9 hours.

Example 13

Copolyimide films were prepared from polyamic acid solutions using thefollowing procedure. The polyamic acid solutions were doctored ontoplate glass and placed in a dust free chamber until they were tack free.The dry polyamic acid films were cured at 100, 200 and 300° C. for 1hour each in air. The thin films were cut into 0.20 inch strips and thetensile properties were determined at several temperatures. Theseproperties are given in Table 1.

                  TABLE 1                                                         ______________________________________                                                 Test      Tensile   Tensile                                            ODPA/BPDA Temperature Strength Modulus                                        ratio (° C.) Ksi Ksi % Elongation                                    ______________________________________                                        100/0 (control)                                                                         23       18.2 ± 1                                                                             468 ± 2                                                                           6.8 ± 1                                  75/25  23 17.6 ± 1.1 443 ± 26 17.1 ± 11                               150 10.6 ± 0.6 306 ± 14 21.6 ± 14                                    177  8.8 ± 0.5 261 ± 27 22.2 ± 25                                   50/50  23 17.4 ± 0.4 451 ± 14 9.5 ± 1                                 150 10.1 ± 0.7 363 ± 19 9.0 ± 6                                      177  9.1 ± 0.7 332 ± 14 5.8 ± 4                                     25/75  23 18.9 ± 0.4 469 ± 7  7.0 ± 1.5                               150 10.0 ± 1.0 297 ± 4  9.3 ± 4                                      177  8.0 ± 0.6 250 ± 20 18.9 ± 15                                   0/100 (control)  23 17.1 ± 2   589 ± 25 4.7 ± 0.8                     150 12.3 ± 1   371 ± 13 3.6 ± 0.5                                    177 11.2 ± 1   354 ± 33 3.4 ± 0.6                                 ______________________________________                                    

Example 14

A Copolyimide film was prepared directly from the reaction mixturecontaining BPDA/ODPA (50/50), 3,4'-ODA copolyimide at a 2% offset ratioaccording to the following procedure. The copolyimide solution wasdoctored onto plate glass and placed in a dust free chamber until it wastack free. The dry copolyimide film was heated at 100, 200 and 300° C.for 1 hour each in air. The thin film was cut into 0.20 inch strips andthe tensile properties were determined at several temperatures. Theresults are given in Table 2.

                  TABLE 2                                                         ______________________________________                                              Test      Tensile  Tensile                                                Casting Temperature Strength Modulus                                          Solvent (° C.) (Ksi) (Ksi) % Elongation Color                        ______________________________________                                        NMP    23       20.6 ± 2                                                                            588 ± 80                                                                          7.2 ± 2                                                                             Dark                                    150 12.6 ± 0.8 369 ± 31 24 ± 15 Orange                               177 11.1 ± 1   382 ± 57 33 ± 20                                   ______________________________________                                    

Example 15

The following procedure was followed to prepare copolyimide films fromthe copolyimide powder. Copolyimide powders prepared at 2% offset weredissolved in a NMP/toluene or mixed xylenes (9/1 weight) solution over a12 hour period at 23° C. to form 10-15% by weight solid solutions. Thesecopolyimide solutions were doctored onto plate glass and placed in adust free chamber until they were tack free. The copolyimide films wereheated under several conditions: 100 and 200° C.; 100 and 225° C.; 100,200, 300° C.; or 100, 225 and 350° C. for 1 hour each in air. The filmswere removed from the glass plates by soaking in water. The thin filmswere cut into 0.20 to 0.75 inch strips and used for adhesive bonding,solvent resistance and the determination of tensile properties. Theunoriented thin film properties for the films cured at 100, 200 and 300°C. for 1 hour each in air are listed in Table 3.

                  TABLE 3                                                         ______________________________________                                                 Test      Tensile   Tensile                                            ODPA/BPDA Temperature Strength Modulus                                        ratio (° C.) (Ksi) (Ksi) % Elongation                                ______________________________________                                        50/50     23       20.6 ± 2                                                                             588 ± 80                                                                          7.2 ± 2                                   150   12.6 ± 0.8 382 ± 57 24 ± 15                                    177 11.1 ± 1 369 ± 31 33 ± 20                                       25/75  23 18.2 ± 2 491 ± 64 25 ± 13                                   150 11.2 ± 1 361 ± 38 24 ± 22                                        177   9.9 ± 0.7 294 ± 14 82 ± 40                                  ______________________________________                                    

Example 16

Neat resin moldings were prepared from the copolyimide powder using thefollowing procedure. The copolyimide powder (2% offset) was placed in astainless steel mold which had been pretreated with a release agent.Various molding conditions (summarized in Table 4) were used to formconsolidated moldings. The glass transition temperature (Tg) wasdetermined from the molding flash using Differential ScanningCalorimetry (DSC) at a heating rate of 20° C. per minute. The resultsare given in Table 4. Neat resin properties of the molded specimens werealso tested. These properties are summarized in Table 5.

                  TABLE 4                                                         ______________________________________                                                                            Tg (° C.)                            ODPA/BPDA Temperature Pressure Time 1st Run                                   Ratio (° C.) (PSI) (Minutes) 2nd Run                                 ______________________________________                                        25/75     300       200      30     236   243                                   25/75 350 200 30 240 245                                                      50/50 225 3000  30 227 251                                                    50/50 250 2000  30 240 251                                                    50/50 300 200 30 248 251                                                      50/50 350 150 30 245 253                                                      75/25 350 200 30 258 259                                                    ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                                               Tensile                                                  ODPA/  Test Modu- Tensile                                                     BPDA Molding Temp. lus Strength K.sub.1C.sup.a G.sub.1C.sup.b                 ratio Conditions (° C.) (GPa) (MPa) (GNm.sup.-3/2) (KJ/m.sup.2)      ______________________________________                                        50/50 250° C.                                                                          23     --    --     3.5    --                                    1/2  hour                                                                     2000 psi                                                                     50/50 300° C.  23 4.23 111.2 4.4 4.6                                    1/2  hour                                                                     200 psi 177 3.16  42.8 -- --                                                 50/50 350° C.  23 4.45 111.2 4.3 4.2                                    1/2  hour                                                                     150 psi 177 3.26  53.1 -- --                                               ______________________________________                                         .sup.a From compact tension specimens.                                        .sup.b From data compact tension and microdumbell.                       

Example 17

Physical and thermal properties were determined for copolyimide (PI)solutions and thin films which were prepared having a 3% offset ratioand endcapped with phthalic anhydride. The inherent viscosities(η_(inh)) were obtained in copolyimide/NMP solutions (0.5 g/dL) at 25°C. as well as for the polyamic acids (PAA). Differential scanningcalorimetry (DSC) was performed on copolyimide films (dried at 100, 200and 300° C. for 1 hour in air) at a heating rate of 20° C./min with theglass transition temperature (Tg) taken at the inflection point in theheat flow vs. temperature curve and the melting temperature (Tm) takenat the minimum of the endothermic depression. Thermogravimetric analysis(TGA) was performed on the polyimide films at a heating rate of2.5°C./min under flowing air and nitrogen. Polymer densities wereobtained at 23° C. using thin films (cured at 100, 200 and 300° C. for 1hour in air) and a density gradient column consisting of aqueous zincchloride. These results are given in Table 6.

                  TABLE 6                                                         ______________________________________                                                             5% Weight                                                  DSC Loss                                                                    ODPA/.BPDA                                                                             η.sub.inh (dL/g)                                                                    Tg     Tm   Air  N.sub.2                                                                            Density                              ratio    PAA    PI     (° C.)                                                                      (° C.)                                                                      (° C.)                                                                      (° C.)                                                                      (g/ml)                             ______________________________________                                        100/0 (control)                                                                        0.23   Ins.   232  291  491  491  1.389 ± 1e.sup.-3                 75/25 0.44 0.37.sup.a 239 -- 474 480 1.376 ± 4e.sup.-4                     50/50 0.40 0.33.sup.  248 -- 484 484 1.376 ± 7e.sup.-4                     25/75 0.44 0.45.sup.a 253 -- 510 508 1.378 ± 2e.sup.-4                     0/100 (control) 0.54 Ins. 260 387 490 493 1.406 ± 6e.sup.-4                50/50 0.60 Ins. 240 315 491 492 >1.45                                         (4,4'-ODA)                                                                  ______________________________________                                         .sup.a 2% offset polyimide polymerized in a 15% solids NMP solution.          Ins.  insoluble                                                          

Example 18

Melt viscosities were run on copolyimides having an offset instoichiometry ranging from 1% to 5% and had been endcapped with phthalicanhydride. The ratio of ODPA to BPDA was 50/50. Table 7 summarizes theresults.

                  TABLE 7                                                         ______________________________________                                        % Offset                                                                              Extrusion Temperature (° C.)                                                             Melt Viscosity (Poise)                              ______________________________________                                        1       290               >6,000,000                                             304 3,951,000                                                                 338 610,000                                                                  2 285 4,028,000                                                                303 603,000                                                                   337 351,000                                                                  3 281 1,318,000                                                                303 311,000                                                                   340 93,000                                                                   4 285 351,000                                                                  303 127,000                                                                   340 30,000                                                                   5 285 269,000                                                                  303 92,000                                                                    337 9,000                                                                  ______________________________________                                    

Example 19

Adhesion testing was conducted using a 50/50 BPDA/ODPA copolyimidehaving a 2% offset in stoichiometry. Lap shear joints were constructedusing titanium (Ti, 6Al-4V) coupons as the substrates. One bonding filmwas solvent cast and dried at 200° C. for 1 hour in air to provide athin film with approximately a 5% volatile content. Another bonding filmwas solvent cast and dried at 100, 200 and 300° C. for 1 hour each inair to provide a film which had less than 0.1% volatiles. Scrim clothsamples were coated several times and dried at 100 and 225° C. for 1hour each in air between coats with a final soak at 300° C. for 30minutes. The bonding conditions and results from this testing are givenin Table 8.

                  TABLE 8                                                         ______________________________________                                                               Test      Bond- Shear                                      Temperature line Strength                                                   Adhesive Bonding Conditions (° C.) (mils) (psi)                      ______________________________________                                        Thin Film                                                                              50 psi         23       2.1   5600                                       ˜5% volatiles 300° C. 150 1.2 5000                              30 minutes 177 1.5 3900                                                      Thin Film 50 psi  23 3.9 4365                                                 <0.1% volatiles 350° C. 150 2.8 3760                                    30 minutes 177 3.9 3360                                                      Scrim Cloth 15 psi/350° C./30 min  23 11.5  4030                         0.3% volatiles 25 psi/350° C./30 min  23 12.0  4405                   50 psi/350° C./30 min  23 13.5  5230                                ______________________________________                                    

Example 20

Matrix composites were prepared using a 50/50 blend of BPDA/ODPA at a 2%offset and endcapping with phthalic anhydride. Iron, diamond dust,Upilex R® plastic powder, quartz, graphite and graphite/coppercombinations were the powders used to prepare the composites. In thisexample, the copolyimide serves as a binder for the particles. Table 9summarizes the fabrication conditions for these composites. Three pointbend geometry testing was performed on the graphite and graphite/coppercomposites at 23° C. The results of this testing are given in Table 10.Parts prepared from these composites could be cut and machined to formvarious ports or molded directly to form different objects for variousunique applications.

                  TABLE 9                                                         ______________________________________                                        Material   Polyimide   Molding Conditions                                                                          Density                                    (total weight %) (total weight %) min/Ksi/° C. (g/cm.sup.3)          ______________________________________                                        Iron (98)  2           30/40/250-350 6.98                                       Diamond Dust (95) 5 30/20/350 2.75                                            Upilex R ® (95) 5 30/10/350 1.41                                          Quartz (95) 5 30/5/350 1.72                                                   Quartz (95) 5 30/10/350 1.71                                                  Quartz (95) 5 30/20/350 1.77                                                  Quartz (90) 10 30/10/350 1.83                                                 Graphite (86.5) 13.5 30/10/250 1.89                                           Graphite/Copper 10 30/1.5/350 1.85                                            (85/5)                                                                        Graphite/Copper 10 30/5/350 2.00                                              (85/5)                                                                        Graphite/Copper 5 30/5/350 2.09                                               (76/19)                                                                     ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                                     Molding   Flexural Flexural                                        Material Composition Conditions Modulus Strength                              (% by weight) min/Ksi/° C. (Msi) (psi) % Strain                      ______________________________________                                        Graphite/PI (86.5/13.5)                                                                    30/10/300 2.36     6130  0.3                                       Graphite/Copper/PI 30/1.5/350 3.00 7610 0.3                                   (85/5/10)                                                                     Graphite/Copper/PI 30/5/350 2.40 5400 0.3                                     (85/5/10)                                                                     Graphite/Copper/PI 30/5/350 2.50 5400 0.3                                     (76/19/5)                                                                   ______________________________________                                         PI  copolyimide                                                          

Example 21

The following procedure was followed to dip coat a copper wire. A 10%solution of the copolyimide in NMP was prepared. A 10 gauge copper wirewas dipped into the solution and dried at 300° C. for 1 hour in air.This process was repeated several times to build up a multi-layerprotective coating. The coated copper wire could be bent without causingthe coating to peel away from the wire.

Example 22

The following procedure was used to prepare a molding of a filledcopolyimide. The 50/50 BPDA/ODPA 2% offset polyimide powder was mixedwith a blend of 15% by weight of graphite powder and 10% by weight ofTeflon® powder. The mixture was blended using a shaker and subsequentlycompression molded at 300° C. for 30 minutes at 200 psi to afford asolid uniform block. The block was machined and cut to various shapes.

Example 23

Substrates were coated using the following procedure. A solutionconsisting of 10% by weight of the 50/50 BPDA/ODPA 2% offset polyimidewas doctored onto clean Kapton® and aluminum foil. The coated substrateswere placed into a dust free chamber until they were tack-free. Thetack-free, coated substrates were then treated at 100, 200 and 300° C.for one hour each in air. The substrates were then folded in half withthe copolyimide to the inside and placed in a hot press forconsolidation. The press was set at 300° C. and 100 psi and the exposuretime was 15 minutes. This yielded a self-bonded material which could notbe torn apart without destroying the substrates.

Example 24

The following procedure was used to mold particles which had been coatedwith the copolyimide to substrates. Graphite powder which had beencoated with a 10% by weight 50/50 BPDA/ODPA 2% offset copolyimide wasplaced in a stainless steel mold. A piece of aluminum foil which hadbeen coated with 50/50 BPDA/ODPA 2% offset copolyimide was placed on topof the graphite powder with the coating facing the graphite powder toform a composite preform. The composite preform was molded at 300° C.and 5000 psi for 30 minutes to form a consolidated graphite part havinga foil backing.

The aluminum foil could not be removed without being destroyed.

Example 25

The following example is for the preparation of a composite from thecopolyimide. A 30% by weight solids in NMP solution of BPDA/ODPA 50/50copolyimide having a 3% offset ratio was used to solution coatcontinuous IM-7 carbon fibers (commercially available from Hercules)creating a 3 inch wide unidirectional tape. This tape was then cut into3×3 inch and 3×6 inch sections (plies) and stacked to form panels whichwere 12 and 24 plies thick. The panels were consolidated at 300° C. and200 psi for 1 hour to yield a consolidated continuous carbon fibercomposite.

Example 26

The following procedure was used to form thermally and mechanicallyreversible gels from the copolyimides. Several liquid solutionsconsisting of 10%, 30% and 60% by weight solids in NMP were preparedfrom 50/50 BPDA/ODPA copolyimides having a 2% offset. The liquidsolutions were made through direct synthesis of the copolyimide and byredissolving the required amount of the copolyimide in the solvent. Theliquid solutions were allowed to stand for 24 hours at room temperaturewhereby a thick gel formed. The gelled solutions were then heated untilthe liquid solution reformed. In addition to heating the gelledsolutions, the 10% and 30% by weight gelled solutions were mechanicallyagitated to reform the liquid solution. The reformed liquid solutionswere allowed to stand at room temperature which caused the gel toreform. As a result, the sol-gel process was shown to be both thermallyand mechanically reversible. This is demonstrated by the DSC data shownin Table 11.

                  TABLE 11                                                        ______________________________________                                        Weight % Solids of Gel                                                                      1st Run Tm (° C.)                                                                   2nd Run Tm (° C.)                           ______________________________________                                        30            119          None Detected                                        60 178 None Detected                                                        ______________________________________                                    

Example 27

Solvent resistance testing was performed on a copolyimide prepared fromBPDA/ODPA (50/50) 2% offset polyimide film which had been dried at 300°C. The thin films were weighed and twisted around a steel paper clipwhich was subsequently placed into a jar containing a specific solventfor 10 days. After removing the films from the jar, they were blotteddry, visually examined, weighed and creased. The results from this testalong with the respective solvents which were used are recorded in Table12.

                  TABLE 12                                                        ______________________________________                                                       Test                                                             Solvent Temp Weight Loss Appearence                                         ______________________________________                                        Water          23° C.                                                                         <0.1%     NCC, Creasible                                 Jet Fuel 23° C. <0.1% NCC, Creasible                                   Toluene 23° C. <0.1% NCC, Creasible                                    MEK 23° C. <0.1% NCC, Creasible                                        Methylene Chloride 23° C. <0.1% NCC, Wrinkled,                            Creasible                                                                  Hydraulic Fluid (TSP Based) 23° C. <0.1% NCC, Creasible                NMP 23° C. 7.5% NCC, Some                                                 Fracture                                                                   THF 23° C. <0.1% NCC., Creasible                                       Ethylene Glycol 23° C. <0.1% NCC, Creasible                          ______________________________________                                         NCC = No Color Change                                                    

Example 28

The following procedure was followed to prepare a sprayable dielectriccoating. A formulated solution of BPDA/ODPA 50/50 2% offset copolyimide(10% solids in NMP) was applied to different substrates using anairbrush. Examples of these substrates include: glass, ceramic,aluminum, Kapton®, copper, Yttrium stabilized zirconia (YSZ), and LeadZirconate Titanate (PZT). The coating was initially dried in air at 44°C. and subsequently at 300° C. The typical coating thickness range wasfrom 0.00025 inches to 0.0005 inches. The coating was found to serve asa good dielectric adhesive which readily accepted the deposition ofgold, copper and aluminum circuitry, showing that the ultra-thin coatingof the copolyimide forms an excellent finish for allowing the attachmentof dissimilar electronic materials to various substrates.

Example 29

Thin film multilayer flexible circuits were prepared using the BPDA/ODPA50/50 2% offset copolyimide (10% solids by weight in NMP) solution as afilm substrate and as a spray, to fabricate multilayer thin films. Theprocess involved metallizing a piece of the copolyimide film by means ofevaporation or sputtering and transferring a circuit pattern to themetallized film by means of a standard photolithography process.

The copolyimide was solvent cast onto a releasable surface such as glassto afford a film thickness ranging from 0.0003 inches to 0.0005 inches.The copolyimide film was initially dried at 44° C. and dried at a finaltemperature of 300° C. for 30 minutes. The film was then metallized andpatterned using a standard photolithography process. After the circuitwas formed, multiple coats of the copolyimide solution (1 part ofBPDA/ODPA 50/50 2% offset to 8 parts of NMP solvent by weight) weresprayed to isolate the newly formed circuit. The sprayed coating wasdried in a similar manner and metallized with 300 Angstroms of chromeand 2,000 Angstroms of gold. A circuit was patterned onto the newlycoated film using the same photolithography process. This process wasrepeated multiple times in order to form a multilayer thin film flexiblecircuit.

Example 30

The following process was used to bond films and foils together.BPDA/ODPA 50/50 2% offset copolyimide (10% solids in NMP) solution wassprayed onto various polyimide films and aluminum/copper foils in orderto bond them together. After the film or foil was sprayed with thecopolyimide, it was dried at 100 and 250° C. for one hour each in air.The film and foil were stacked and hot pressed at a temperature of 300°C. using 100 psi for 15 minutes to secure the bond. The bonded filmcould be flexed without delamination showing that it could be used inthe formation of ultra-thin multilayer polyimide metal-film laminates.

I claim:
 1. A copolyimide having the repeat unit: ##STR2##
 2. Acopolyimide according to claim 1 wherein the copolyimide is terminatedwith maleic anhydride.
 3. A copolyimide according to claim 1 wherein thecopolyimide is terminated with phenylethynyl anhydride.
 4. A copolyimideaccording to claim 1 wherein the copolyimide is terminated with ethynylanhydride.
 5. A copolyimide according to claim 1 wherein the copolyimideis terminated with nadic anhydride.
 6. A copolyimide according to claim1 wherein the copolyimide is terminated with vinylic anhyrdride.
 7. Acopolyimide according to claim 1 wherein the copolyimide is terminatedwith benzocyclobutane anhydride.
 8. A copolyimide according to claim 1wherein the copolyimide is terminated with phenylethynyl amine.
 9. Acopolyimide according to claim 1 wherein the copolyimide is terminatedwith ethynylaniline.
 10. A copolyimide according to claim 1 wherein thecopolyimide is terminated with vinylaniline.
 11. A copolyimide accordingto claim 1 wherein the copolyimide is terminated with allylaniline. 12.A copolyimide according to claim 1 prepared by reacting4,4'-oxydiphthalic anhydride with 3,4,3,4'-biphenyltetracarboxylicdianhydride and 3,4-oxydiisocyanate.
 13. An article prepared from thecopolyimide according to claim 1, wherein the article is selected fromthe group consisting of: a foam, a tack-free recastable film, a particlefilled thin film and a particle filled thin coating.
 14. A particlefilled thin film prepared from the copolyimide according to claim 1,wherein the particle is selected from a group consisting of: metal,plastic, ceramic, carbon and boron.
 15. A particle filled thin coatingprepared from the copolyimide according to claim 1, Wherein the particleis selected from a group consisting of: metal, plastic, ceramic, carbonand boron.
 16. A copolyimide according to claim 1 prepared by reacting acorresponding tetra acid of 4,4'-oxydiphthalic anhydride with acorresponding teta acid of 3,4,3',4'-biphenyltetracarboxylic dianhydrideand 3,4'-oxydianiline.
 17. A copolyimide according to claim 1 preparedby reacting a corresponding di (acid-ester) of 4,4'-oxydiphthalicanhydride with a corresponding di(acid-ester) of3,4,3',4'-biphenyltetracarboxylic dianhydride and 3,4'-oxydianiline.